1. The Field of the Invention
The present invention relates to vertical diodes and, more specifically, to vertical diodes with low series resistance formed on a silicon wafer.
2. The Relevant Technology
One of the common trends in the electronics industry is the miniaturization of electronic devices. This trend is especially true for electronic devices operated through the use of semiconductor microchips. Microchips are commonly viewed as the brains of most electronic devices. In general, a microchip comprises a small silicon wafer upon which can be built thousands of microscopic electronic devices that are integrally configured to form electronic circuits. The circuits are interconnected in a unique way to perform a desired function.
With the desire to decrease the size of electronic devices, it is also necessary to decrease the size of the microchip and electronic devices thereon. This movement has increased the number and complexity of circuits on a single microchip.
One common type of electronic device found on a microchip is a diode. A diode functions as a type of electrical gate or switch. An ideal diode will allow an electrical current to flow through the diode in one direction but will not allow an electrical current to flow through the diode in the opposite direction. In conventional diodes, however, a small amount of current flows in the opposite direction. This is referred to as current leakage.
Conventional diodes are typically formed from a silicon material that is modified through a doping process. Doping is a process in which ions are implanted within the silicon. There are two general types of dopants: P-type dopants and N-type dopants. P-type dopants are materials that, when implanted within the silicon, produce regions referred to as holes. These holes can freely accept electrons. In contrast, N-type dopants are materials that, when implanted within silicon, produce extra electrons. The extra electrons are not tightly bound and thus can easily travel through the silicon. In general, a diode is formed when a material doped with a P-type dopant is connected to a material doped with an N-type dopant.
Conventional diodes are configured by positioning the two opposing doped materials side by side on a microchip. This side-by-side positioning, however, uses a relatively large amount of surface space on the microchip. As a result, larger microchips are required.
Furthermore, for a diode to operate, each side of the diode must have an electrical connection that either brings electricity to or from the diode. The minimal size of each side of the diode is in part limited in that each side must be large enough to accommodate an electrical connection. Since conventional diodes have a side-by-side configuration with each side requiring a separate electrical connection, the ability to miniaturize such diodes is limited. In addition, the requirement of having side-by-side electrical connections on a single diode increases the size and complexity of the microchip.
Attempts have been made to increase the efficiency and current flow rate through a diode so as to speed up the microchip. In one attempt to accomplish this end, one of the sides of the diode is heavily doped and the other side of the diode is lightly doped. The lightly doped side limited the current, and the heavily doped side increased the reverse bias leakage. Thus, such a configuration produces minimal gain.
Other attempts have been made to decrease the resistance in the above-discussed diode by increasing the dopant concentration on the lightly doped side of the diode. As the dopant concentration is increased, however, current leakage in the diode increases. In turn, the current leakage decreases the current efficiency and functioning of the microchip.